Method and system for antenna interference cancellation

ABSTRACT

A wireless communication system can comprise two or more antennas that interfere with one another via free space coupling, surface wave crosstalk, dielectric leakage, or other interference effect. The interference effect can produce an interference signal on one of the antennas. A cancellation device can suppress antenna interference by generating an estimate of the interference signal and subtracting the estimate from the interference signal. The cancellation device can generate the estimate based on sampling signals on an antenna that generates the interference or on an antenna that receives the interference. The cancellation device can comprise a model of the crosstalk effect. Transmitting test signals on the communication system can define or refine the model.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application Ser. No. 60/520,592, entitled “Improved Performanceof Closely Spaced Antennas,” and filed Nov. 17, 2003. The contents ofU.S. Provisional Patent Application Ser. No. 60/520,592 are herebyincorporated by reference.

This application is related to U.S. Nonprovisional patent applicationSer. No. 10/108,598, entitled “Method and System for Decoding MultilevelSignals,” filed on Mar. 28, 2002, and U.S. Nonprovisional patentapplication Ser. No. 10/620,477, entitled “Adaptive Noise Filtering andEqualization for Optimal High Speed Multilevel Signal Decoding,” filedon Jul. 15, 2003, and U.S. Nonprovisional patent application Ser. No.10/911,915, entitled “Method and System for Crosstalk Cancellation,”filed on Aug. 5, 2004. The contents of U.S. patent application Ser. No.10/108,598 and U.S. patent application Ser. No. 10/620,477 and U.S.patent application Ser. No. 10/911,915 are hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to the field of wireless communications,and more specifically to improving the signal performance of acommunication system having two or more adjacent antennas bycompensating for crosstalk and coupling interference that can impairantenna performance.

BACKGROUND

Heightened consumption of communication services fuels a need forincreased data carrying capacity or bandwidth in wireless communicationsystems. Phenomena known as crosstalk and interference often occur inthese communication systems and can impair high-speed signaltransmission and thus limit wireless communication bandwidth to anundesirably low level.

Crosstalk and related interference are conditions that arise incommunication systems wherein a signal in one communication channel orantenna interferes with or bleeds into another channel or antenna or anassociated structure, housing, material, active device, or conductor.Such interference may occur due to a variety of effects, includingcurrent leakage, surface wave propagation, line interference, andelectromagnetic coupling.

Crosstalk is emerging as a significant barrier to increasing throughputrates of wireless communications systems. When not specificallyaddressed, crosstalk often manifests itself as noise. In particular,crosstalk degrades signal quality by increasing uncertainty in receivedsignals, thereby making reliable communications more difficult andcausing data errors to occur with increased probability. In other words,crosstalk typically becomes more problematic at increased data rates.Not only does crosstalk reduce signal integrity, but additionally, theamount of crosstalk often increases with bandwidth, thereby makinghigher data rate communications more difficult.

In a typical wireless communication system, circuit boards, connectors,and transmission lines handle the incoming and outgoing communicationsignals that enter or leave the system via communication antennas. Athigh communication speeds, the conductive paths of the system's circuitboards, connectors, and transmission lines pickup and radiateelectromagnetic energy that can interfere with the performance of thesystem's receiving and sending antennas. The radiated energy from oneantenna or an associated conductive channel undesirably couples into oris received by another antenna or its associated channel. Thisundesirable transfer of signal energy, known as “crosstalk” or“interference,” can compromise signal or data integrity. Crosstalktypically occurs in a bidirectional manner in that a single antenna orchannel can both radiate energy to one or more other antennas orchannels and receive energy from one or more other antennas or channels.

Compact wireless communication devices are particularly susceptible toantenna-to-antenna crosstalk. The close proximity of the antennas insuch systems can intensify the crosstalk effect and cause acute signaldegradation. Such interference can affect multiple-antenna wirelessapplications, whether each antenna carries the same payload or adistinct payload. Further, interference between antennas can impairperformance whether each antenna operates at the same frequency or at aunique frequency. In applications involving global positioning sensors(“GPS”), wireless fidelity (“WiFi”), “Bluetooth,” or another wirelessstandard, each of two interfering antennas of a wireless device mayoperate at a different frequency and support one of these services. Inantenna diversity systems and other applications having two or moreantennas that each carries the same payload, crosstalk coupling candistort the radiation pattern of each antenna. The radiation pattern canalso be affected whether the antennas operate in band or out of band,for example in applications other than antenna diversity.

Antenna diversity typically involves using two or more antennas toreceive multiple instances of the same signal. The resulting signalredundancy enables the system to be robust against many factors that candegrade signal reliability, such as antenna type, antenna orientation,and beam obstacles. However, interference among the multiple antennasthat are typically associated with antenna diversity can defeat thetechnique's benefits when the antennas are closely spaced to oneanother. Additionally, from a power budget perspective, it is beneficialto avoid unnecessarily resorting to activating dormant antennas forincreased gain.

In multi-antenna systems, whether the antennas carry distinct orindistinct signals, maintaining an adequate level of antenna isolationis generally desirable. A minimum isolation of 15 dB is usuallyconsidered adequate for most applications. Using conventionaltechnology, such isolation can be difficult to attain in miniaturizeddevices, such as handhelds, in which the antennas are physically closetogether. Without adequate isolation, reducing the spacing betweenantennas can negatively impact gain, directivity, throughput, beamshape, reach, efficiency, and receiver sensitivity. Because the amountof antenna-to-antenna coupling increases with closer antenna spacing,distances of 17-33% of the wavelength (“λ”), i.e. λ/6 to λ/3, are oftenconsidered a compromise between antenna isolation and compactness.

In an effort to achieve increased miniaturization, conventionalcanceller systems have been used to provide a limited level of isolationbetween interfering antennas. One type of conventional canceller systemsamples an interfering signal from a transmitting antenna and generatesa cancellation signal that is adjusted in magnitude and phase to cancelleakage signals impinging on an adjacent antenna. This conventionaltechnology is generally limited to addressing leakage signals, which arehigh-frequency currents, and usually does not adequately address otherforms of interference such as surface wave crosstalk and free spacecoupling. Surface wave crosstalk can occur when electromagnetic wavespropagate along the surface of a circuit board, mounting, or otherstructure that is proximate to two or more adjacent antennas. Via freespace coupling, the electromagnetic field patterns of the adjacentantennas can undesirably distort or interact with one another in an openair propagation medium.

Conventional canceller systems may also attempt to maintain isolation ofthe signals that a transmit antenna generates to reduce the mixing ofoutgoing signals with incoming signals on a nearby receiving antenna.However, such conventional canceller systems generally do not adequatelyaddress all of the phenomena that can cause antenna-to-antennainterference or crosstalk. For example, the physical presence of thereceive antenna can distort the radiation pattern of the system, even ifthe receive antenna is in a passive or dormant mode. This distortion cancause a receive antenna to undesirably radiate energy or can warp thefield pattern of a nearby transmitting antenna. The presence of onereceive antenna can also distort the receptive pattern of anotherreceive antenna. Conventional canceller technologies generally neglectsuch secondary radiation effects that may occur in free space. In otherwords, these conventional canceller systems typically apply cancellationto address leakage-type crosstalk occurring within a device, but oftendo not adequately address crosstalk between two antenna field patternsin free space.

To address these representative deficiencies in the art, what is neededis a capability for crosstalk cancellation between two or more antennasdisposed in physical proximity to one another. A need also exists for acapability to cancel crosstalk occurring between two antennas throughfree space coupling or via propagation of surface waves. Suchcapabilities would facilitate higher bandwidth and increased signalfidelity in wireless communication applications that may involve compactdevices.

SUMMARY OF THE INVENTION

The present invention supports compensating for signal interference,such as crosstalk, occurring between two antennas or among more than twoantennas. Compensating for crosstalk can improve signal quality andenhance bandwidth or information carrying capability in a wirelesscommunication system.

A communication signal transmitting on one antenna can couple or imposean unwanted signal, such as interference or crosstalk, onto anotherantenna. The antenna carrying the communication signal can be referredto as the transmitting antenna, while the antenna carrying the imposedcrosstalk can be referred to as the recipient antenna. In a wirelesscommunication system, such coupling can interfere with and degrade theperformance of either or both antennas, for example limiting bandwidthor degrading signal fidelity.

In one aspect of the present invention, a cancellation device can applya cancellation signal to the recipient antenna, which typically receivesan interference signal imposed by the transmitting antenna. Thecancellation signal can suppress, cancel, reduce, minimize, or negate,or otherwise compensate for, the interference signal, thereby enhancingisolation between the antennas and improving performance. Thecancellation device can generate, compose, or produce the cancellationsignal based on signals sampled or tapped either from the transmittingantenna or from the recipient antenna.

In another aspect of the present invention, the cancellation device cangenerate the cancellation signal by sampling the interference signalfrom the recipient antenna and processing the sample signal. Processingthe sample signal can comprise adjusting the phase and the amplitude ofthe sample signal with a signal processing circuit to provide acancellation signal that matches the interference signal. Adjusting thephase and amplitude of the sample signal can comprise slightly delayingin time an oscillation or cycle of the signal or slightly impeding thespeed of propagation of the sample signal, for example with a variablephase adjuster. Adjusting the amplitude of the sample signal cancomprise amplifying, scaling, or intensifying the sample signal, forexample with a variable gain amplifier. The cancellation device canapply the cancellation signal to the recipient antenna to cancel theinterference signal carried thereon. For example, the cancellationdevice can subtract the cancellation signal from the interference signalvia a coupler that introduces the cancellation signal onto a feed lineof the recipient antenna. The cancellation device can comprise acontroller that dynamically controls, tunes, or adapts the phase andamplitude adjustments to refine or update the effectiveness of theinterference cancellation. The cancellation device can gaugecancellation effectiveness by monitoring the level of residual orun-cancelled interference energy that exists on the recipient antennafollowing cancellation. The controller can use the monitored energy orpower level as a feedback signal for refining the phase and amplitudeadjustments. During interference cancellation, the recipient antenna canbe in a dormant or passive state, for example refraining fromtransmitting communication signals, while the transmitting antenna is inan active state of transmitting communication signals.

In another aspect of the present invention, the cancellation device cangenerate a cancellation signal by sampling the communication signal onthe transmitting antenna and processing that sample signal. Processingthe sample signal can comprise feeding the sample signal into a model ofthe interference effect. The model can generate and output thecancellation signal as an estimate or emulation of the interferencesignal. The cancellation device can cancel a substantial portion of theinterference by applying the cancellation signal to the recipientantenna, for example, by subtracting the cancellation signal from thesignals that the recipient antenna carries. The cancellation device cancomprise a controller that dynamically adjusts or adapts the model torefine the cancellation signal, thereby increasing cancellationeffectiveness or maintaining cancellation effectiveness in a dynamicoperating environment. The controller can monitor residual interferenceenergy on the recipient antenna and adjust the model to minimize themonitored energy. The cancellation device can inject test signals intothe antenna system and monitor the interference that these test signalsproduce. The controller can analyze interference stimulated by the testsignals and refine the model based on the analysis.

The discussion of canceling or correcting interference presented in thissummary is for illustrative purposes only. Various aspects of thepresent invention may be more clearly understood and appreciated from areview of the following detailed description of the disclosedembodiments and by reference to the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the invention can be better understood with reference tothe following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of exemplary embodiments of the presentinvention. Moreover, in the drawings, reference numerals designatecorresponding parts throughout the several views.

FIG. 1 is an illustration of an exemplary implementation of twocrosstalk cancellers applied to two antennas in accordance with anembodiment of the present invention.

FIG. 2 is a functional block diagram of an exemplary crosstalk cancellerin a wireless communication system in accordance with an embodiment ofthe present invention.

FIGS. 3A and 3B are illustrations of exemplary simulation results for atwo-antenna system before and after crosstalk cancellation in accordancewith an embodiment of the present invention.

FIGS. 4A, 4B, and 4C are illustrations of simulated antenna fieldpatterns for a single antenna that is inherently isolated, a two-antennasystem before crosstalk cancellation, and a two-antenna system aftercrosstalk cancellation in accordance with an exemplary embodiment of thepresent invention.

FIG. 5A is an illustration of an exemplary system comprising two patchantennas in accordance with an embodiment of the present invention.

FIG. 5B is a graph of representative signal plots for the patch antennasystem prior to interference cancellation in accordance with anembodiment of the present invention.

FIGS. 6A and 6B are representative signal plots for a pair of patchantennas before after interference cancellation in accordance with anembodiment of the present invention.

FIG. 7 is an illustration of an exemplary implementation of a systemcomprising two crosstalk cancellers coupled in a parallel arrangementbetween two antennas in accordance with an embodiment of the presentinvention.

FIG. 8 is a functional block diagram of an exemplary system havingcrosstalk cancellers coupled between two antennas in accordance with anembodiment of the present invention.

FIG. 9 is a graph of an exemplary family of curves of interferencecoupling between two antennas as a function of frequency for variousphase alignment values in accordance with an embodiment of the presentinvention.

FIG. 10 is a flow chart illustrating an exemplary process for cancelingcrosstalk or interference on an antenna according to an embodiment ofthe present invention

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention supports canceling crosstalk or compensating forinterference associated with two or more antennas in a wirelesscommunication system. An exemplary method and system for crosstalkcancellation can enhance signal performance for two antennas that aredisposed in close proximity to one another, for example as components ina compact wireless device, such as a portable or handheld communicationdevice.

This invention can be embodied in many different forms and should not beconstrued as limited to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thosehaving ordinary skill in the art. Furthermore, all “examples” givenherein are intended to be non-limiting, and among others supported byexemplary embodiments of the present invention.

Turning now to FIG. 1, this figure illustrates an exemplarycommunication system 100 having two antennas 110, 115 in close proximityto one another with a crosstalk canceller 175 a, 175 b coupled to thefeed line 160, 165 of each antenna 110, 115.

The system 100 typically operates with one of the two antennas 110, 115dormant while the other antenna 110, 115 actively transmits a signal.The mode of each antenna 110, 115 can change during normal operation ofthe system. That is, one of the antennas 110, 115 can be in a passive,idle, dormant, sleep or non-transmission mode, while the other antenna110, 115 is in a transmission mode. In the illustrated operationalstate, the antenna 115 is in the active mode while the antenna 110 is inthe dormant mode. The antenna 115 transmits communication signals andimposes interference on the antenna 110. Thus, in the illustrated state,the antenna 115 is referred to as the transmitting antenna 115. And, theantenna 110 is referred to as the recipient antenna 110 that receivesinterference from the transmitting antenna 115.

The transfer or coupling of signal energy from the transmitting antenna115 to the dormant recipient antenna 110, in the form of crosstalkinterference 180, 185, 190, can impair the performance of thetransmitting antenna 115. Among other detrimental effects, the unwantedtransfer of radiant energy can distort the active field pattern of thetransmitting antenna 115.

The canceller 175 a cancels the crosstalk interference 180, 185, 190 onthe dormant recipient antenna 110 that the active transmitting antenna115 imposes on the recipient 110. While the transmitting antenna 115 isactive, the canceller 175 b remains passive or does not provide activecancellation.

In the opposite operational state (not shown), antenna 115 is dormantand antenna 110 is active. In this state, canceller 175 b cancelsinterference that antenna 110 imposes on antenna 115, and canceller 175a is passive.

If both antennas 110, 115 are in an active state, then both cancellers175 a, 175 b are typically off or in a passive mode. Both antennas 110,115 may be simultaneously transmitting a common payload to enhance theoverall gain of the system 100, for example. Thus, the cancellationconfiguration of the system 100 can provide interference cancellation indiversity antenna systems wherein one or more antennas are transmittingduring a time period that at least one other system antenna is dormant,passive, or in a non-transmitting state. A compact communication device,such as a cell phone, GPS, radio, walkie-talkie, portable computingdevice, laptop computer, palmtop computing system, etc., can comprisethe system 100. Such a communication device can further comprise aduplexer and an associated power amplifier (“PA”), transmitterelectronics, and receiver electronics (not shown) coupled to the antennafeed lines 165, 160.

The cancellers 175 a, 175 b can reduce or cancel various forms ofinterference or crosstalk 180, 185, 190 that can impair operation of thesystem's antennas 110, 115 and compromise signal fidelity. Exemplaryforms of such crosstalk or interference can include surface waves 190,free space coupling 180, and dielectric leakage 185. Such crosstalk 180,185, 190 can occur in either or both directions during operation of thesystem 100. Thus, each of the antennas 110, 115 can be an interferencegenerator and an interference recipient. That is, each of the twoantennas 110, 115 can be both a crosstalk “aggressor” and a crosstalk“victim.” For example, the transmitting antenna 115 can impose aninterference signal on the dormant recipient antenna 110. The dormantantenna 110 may radiate the imposed interference back to thetransmitting antenna 115, for example as a standing wave, in a mannerthat interferes with the field pattern of the transmitting antenna 115.

Surface waves 190, which are typically electromagnetic signals, canpropagate along the surface of a dielectric material from thetransmitting antenna 115 to the dormant recipient antenna 110. Forexample, each of the antennas 110, 115 can be mounted on a circuit boardsubstrate wherein the feed lines 160, 165 pass through a via orthrough-hole of the circuit board. The surface waves 190 can propagateon the surface of the circuit board, which typically comprisesdielectric material such as resin or ceramic. This unwanted transfer ofenergy can negatively impact the signal performance of the system 100.The canceller 175 a can cancel such surface wave crosstalk orinterference 190.

Free space coupling 180 is the coupling of RF electromagnetic signals inthe free space medium of open air between the antennas 110, 115. Thedormant antenna 110 can draw RF energy from the transmitting antenna115. The presence of the dormant antenna 110 in the vicinity of thetransmitting antenna 115 can undesirably distort the electromagneticfield pattern of the transmitting antenna 115. Such crosstalk orinterference can negatively impact the transmitting antenna'sperformance if left unchecked. The canceller 175 a can enhance antennaisolation by canceling interference due to free space coupling 180.

Dielectric leakage crosstalk or interference 185 can also compromisesignal integrity of the antennas 110, 115. Dielectric leakage 185 canoccur when an imperfect insulator, such as a flawed dielectric material,allows bleed-through of RF electromagnetic signals. A portion of thebleed-through RF signal may find a path to the dormant antennas 110, 115and interfere with the antenna's intended signals. The canceller 175 acan cancel dielectric leakage crosstalk or interference 185.

The system's cancellers 175 a, 175 b can address and cancel crosstalk orinterference resulting from one or more phenomena, such as surface wavecoupling 190, free space coupling 180, and dielectric leakage 185 (anon-exhaustive list). Each antenna 110, 115 has a canceller 175 a, 175 bcoupled to its respective feed line 160, 165. As discussed above, eachof the cancellers 175 a, 175 b provides active cancellation during timeperiods that the antenna 110, 115 to which it is connected is dormantand the other antenna 110, 115 is active. By canceling the crosstalkinterference effects 180, 185, 190, these cancellers 175 a, 175 bimprove the level of isolation between the antennas 110, 115. Decouplingthe respective signals of the antennas 110, 115 provides improvedintegrity of the transmitted communication signals and improved antennaradiation patterns. Such improvements enhance efficiency, directivity,beam shape, throughput, and reach.

Each canceller 175 a, 175 b taps off or samples a portion of theinterfering signal on its respective feed line 160, 165 as a referencesignal. Based on this reference signal, each canceller 175 a, 175 bgenerates a cancellation signal that is applied to its respective feedline 160, 165. Thus, when the antenna 110 is dormant and the antenna 115is actively transmitting communication signals (as illustrated),canceller 175 a samples the interference on the feed line 160 and usesthe sampled signal as a reference signal. Based on processing of thisreference signal, the canceller 175 a generates a cancellation signaland applies that cancellation signal to the feed line 160.

The application of the cancellation signal by canceller 175 a to feedline 160 cancels or reduces the interference signals that thetransmitting antenna 115 may otherwise impose on the dormant antenna110. The canceller 175 a adjusts the magnitude, phase, and timing of thegenerated cancellation signal to cancel the interfering signal on thefeed line 160. That is, the canceller 175 a samples the interferingsignals or waveforms on the feed line 160 and composes a cancellationsignal having suitable magnitude, phase, and timing characteristics thatnegate, cancel, or destructively interfere with the crosstalkinterference on the antenna 110.

Turning now to FIG. 2, this figure illustrates a functional blockdiagram of an exemplary crosstalk canceller 175 a in a wirelesscommunication system 100. The system 100, which can be the system 100illustrated in FIG. 1, comprises two cancellers 175 a, 175 b, eachcoupled to the feed line 160, 165 of its respective antenna 110, 115.While both cancellers 175 a, 175 b typically comprise the samefunctional components, for clarity of explanation, FIG. 2 illustrates anexemplary functional block diagram of the canceller 175 a but not of thecanceller 175 b. Thus, the two cancellers 175 a, 175 b can be two copiesof a standardized module.

It will be appreciated by those skilled in the art that the division ofthe system 100 and the crosstalk canceller 175 a into functional blocks,modules, and respective sub-modules as illustrated in FIG. 2 (andsimilarly the system 700 illustrated in FIG. 8 and discussed below) areconceptual and do not necessarily indicate hard boundaries offunctionality or physical groupings of components. Rather,representation of the exemplary embodiments as illustrations based onfunctional block diagrams facilitates describing an exemplary embodimentof the present invention. In practice, these modules may be combined,divided, and otherwise repartitioned into other modules withoutdeviating from the scope and spirit of the present invention.

The canceller 175 a comprises a phase adjuster 220, a delay adjuster225, a variable gain amplifier (“VGA”) 260, two splitters 210, 230, asubtraction node 290, a power detector 240, and a controller 250. Thesplitter 210 samples the interfering signal exciting theotherwise-passive dormant antenna 110. A signal processing circuit 275,comprising the phase adjuster 220 and the VGA 260, processes the samplesignal or reference by respectively adjusting sample signal's phase andamplitude. The summation node 290 applies the phase-shifted andamplitude-adjusted signal that is output by the signal processingcircuit 275 to the feed line 160 of the dormant antenna 110, therebycanceling the interference. The delay adjuster 225 times thecancellation signal and the interference signal for coincidence at thedormant antenna 110. The splitter 230 samples the signal on the feedline 160 resulting from applying cancellation to the crosstalk. Thepower detector 240 measures the power level of this residual,un-canceled signal and provides the resulting measurement to thecontroller 250 as a feedback control signal. Based on this energy orpower measurement, the controller 250 dynamically adjusts or tunes theVGA 260, the delay adjuster 225, and the phase adjuster 220 to refinethe cancellation of interference. The illustrated functional blocks ofthe canceller 175 a will now be discussed individually in furtherdetail.

The splitter 210, the splitter 230, and the summation junction 290 caneach comprise a coupler. The term “coupler,” as used herein, refers to adevice that couples electrical or electromagnetic signals into or out ofa signal channel. The exemplary couplers 210, 230, 290 of the system 100comprise three ports. Two of the ports connect to transmission line 160,while the third port passes the signals that the coupler 210, 230, 290introduces onto or extracts from the transmission line 160. As will bediscussed in further detail below, the canceller's couplers 210, 230,290 extract sample and feedback signals from the feed lines 160, 165 andintroduce cancellation signals onto the feed lines 160, 165.

The splitter 210 that is adjacent to the dormant antenna 110 samples theinterference signals coupled onto this antenna 110 from the adjacenttransmitting antenna 115 via free space coupling 180 or other crosstalkeffect. That is, the splitter 210 taps off a portion of the signalenergy that transfers from the radiant antenna 115 to the passiverecipient antenna 110 as a result of the close proximity of these twoantennas 110, 115. Thus, the splitter 210 acquires a reference signalrepresentative of the interference. The canceller 175 a processes thisacquired reference signal, via the signal processing circuit 275 togenerate a cancellation signal that, when introduced back onto theantenna feed line 160, negates the interference.

In one exemplary embodiment of the present invention the splitter 210 isa passive directional coupler. In an alternative embodiment of thepresent invention, the splitter 210 can comprise an active circuit. Thesplitter 210 typically exhibits relatively high input impedance at thetap-off point. For example, the splitter 210 can provide 50 ohms ofimpendence to match the impedance characteristics of the other discreetcomponents of the canceller 175 a. That is, the components of thecanceller 175 a can be impedance matched at 50 ohms or another suitableimpedance characteristic value.

The impedance characteristics of the splitter 210 support operating theantenna 110 in either the dormant or active mode. At the tap-off, thesplitter 210 should have a high impedance to avoid affecting the feedthrough line characteristic impedance. When the antenna 110 is in theactive mode of purposely transmitting signals (opposite the illustratedoperating state), the canceller 175 a is in a passive or off mode,typically without producing cancellation signals. To support antennaoperation when the canceller 175 a is in such a passive mode, thesplitter 210 preferably introduces minimal or essentially no loss intothe signal path of the antenna feed line 160. That is, the splitter 210avoids contributing excessive loss to the signal path that couldencumber active performance of the antenna 110. Excessive loss in thesignal path of the feed line 160 can impair transmitted or receivedsignals and cause degradation in receiver sensitivity.

To further support operating the antenna 110 in both an active and apassive mode, the splitter 210, the splitter 230, the summation node 290and the delay adjuster 225, as well as any other components in signalpath of the feed line 160, are bidirectional.

In one exemplary embodiment of the present invention, the signal path ofthe feed line 160 comprises loss compensation to compensate for anycomponents in the signal path that introduce loss. Increasing the gainof the PA or a low noise amplifier (“LNA”) can provide losscompensation. A gain block usually cannot be introduced between theantenna 110 and the duplexer because most gain blocks are unidirectionaldevices and therefore affect the bi-directionality of the system.

In one exemplary embodiment, canceller 175 a is introduced between thePA and the duplexer. In this arrangement, the LNA path remains untouchedand will not suffer from the loss hit of the canceller 175 a. However, again block may need to be introduced at the PA side before the cancellersystem 175 a.

In another exemplary embodiment, the canceller system 175 a has a bypassmode. When the canceller 175 a is off, the signal going through the feedline 160 bypasses the canceller 175 a via the bypass mode. Using abypass configuration is typically the preferred approach to address lossissues, as the bypass circumvents any need to improve the gain of the PAand the LNA.

Referring now to the illustrated operational mode, the phase adjuster220 receives the sampled signal from the splitter 210 and adjusts thephase to provide a phase match at the summation node 290 between thephase of the interference signal propagating on the transmit/receivesignal path of the feed line 160 and the cancellation signal. That is,the phase adjuster 220 provides phase synchronization or alignmentbetween the cancellation signal that is applied to the feed line 160 andthe interference that is on the feed line 160.

In one exemplary embodiment, the phase adjuster 220 adjusts the phase ofthe cancellation signal so that the cancellation signal is 1800 out ofphase with the interference at the point of application, which cancomprise a summation node 290. If the cancellation signal is in phasewith the interference, the summation node 290 subtracts the cancellationsignal from the interference (as illustrated). On the other hand, if thecancellation signal is 180° out of phase with respect to theinterference, the summation node 290 adds these signals to one another.

In one exemplary embodiment of this invention the phase shifter 220comprises quadrature hybrids and four silicon hyper-abrupt junctionvaractor diodes, supported by typical resistors, inductors, andcapacitors. In one embodiment, the phase shifter 220 comprises an activecircuit.

The VGA 260 receives the phase shifted or matched cancellation signalfrom the phase adjuster 220 and matches the signal's amplitude to theinterference signal propagating on the feed line 160 of the dormantantenna 110 at the summation node 290. That is, the VGA 260 amplifiesthe cancellation signal to provide an amplitude or magnitude thatmatches the interference on the feed line 160.

The summation node 290, which applies the cancellation signal to thefeed line 160, can be a passive directional coupler or an activecircuit. As discussed above regarding the splitter 210, the summationnode 290 should not introduce significant impedance mismatch to thetransmit/receive path of the antenna feed line 160.

The controllable delay adjuster 225 matches the group delay of theinterference signal propagating through the path of the feed line 160 tothe group delay of the cancellation signal that propagates through thepath of the signal processing circuit 275. That is, the delay adjuster225, which may also be referred to as an adjustable delay, compensatesfor the signal delay that occurs between the splitter 210 and thesummation node 290 along the feed line path relative to the signal delaythat occurs between the splitter 210 and the summation node 290 in thesignal processing circuit 275.

The splitter 230 samples the cancelled signal and feeds it to the powerdetector 240. That is, the splitter 230 provides a sample of theresidual signals on the feed line 160 that result from applying thecancellation signal to the interference at the node 290. If thecancellation is effective, the residual signals have less power orenergy than if the cancellation is ineffective. The power detector 240monitors this cancelled signal and feeds the monitored power to thecontroller 250 as a feedback signal that provides an indication ofcancellation effectiveness. The controller 250 adapts and controls theVGA 260, the phase adjuster 220, and the delay adjuster 225 according tothe feedback to provide a cancellation signal that adequately cancels ornegates crosstalk interference on the feed line 160 and the antenna 110.

More specifically, the controller 250 learns the values of the phase,the delay, and the gain that provide minimal energy on the feed line160. The phase, the delay, and the gain are adjusted to empiricallyreduce the amount of interference to a predetermined or minimal level.Phase or delay misalignments and magnitude mismatches can adverselyaffect the improvements in the overall transmitted signal quality on thetransmitting antenna 115. That is, the controller 250 manipulates theVGA 260, the delay adjuster 225, and the phase adjuster 220 to identifyoperating points for each of these devices that minimize the signalpower on the feed line 160 during time periods that the antenna 110 isdormant and should not be transmitting RF energy. Minimizing signalpower of the dormant antenna 110 and its feed line 160 minimizes theperturbation that this antenna 110 causes on the transmitting antenna115, which is purposely handling communication signals.

The controller 250 comprises logical elements, such as hardwired, fixed,or programmable logic. The controller 250 usually comprises amicrocontroller, microprocessor, microcomputer, or other computingprocessor, such as an application specific integrated circuit (“ASIC”).In addition to such logical elements, the controller can comprisesupporting circuitry, interface electronics, power supplies, and memory,for example.

Commonly owned U.S. Nonprovisional patent application Ser. No.10/108,598, entitled “Method and System for Decoding Multilevel Signals”and filed on Mar. 28, 2002, discloses a viable exemplary system andmethod for assessing signals. Commonly owned U.S. Nonprovisional patentapplication Ser. No. 10/620,477, entitled “Adaptive Noise Filtering andEqualization for Optimal High Speed Multilevel Signal Decoding” andfiled on Jul. 15, 2003, discloses a viable exemplary system and methodfor controlling device parameters of the phase adjuster 220, the VGA260, and the delay adjuster 225. The disclosures of U.S. patentapplication Ser. No. 10/108,598 and U.S. patent application Ser. No.10/620,477 are hereby fully incorporated by reference. One or more ofthe phase adjuster 220, the VGA 260, and the delay adjuster 225 can eachbe controlled and/or adjusted using a method and/or system disclosed inU.S. patent application Ser. No. 10/108,598 or U.S. patent applicationSer. No. 10/620,477. The parameters of these devices 220, 260, 225 canbe determined by treating each device parameter as a variable that isswept through its range of potential values following the disclosure ofthese patent applications, for example.

Turning now to FIGS. 3A and 3B, these figures illustrate a simulation ofan antenna system 300 before and after canceling crosstalk interferenceaccording to an exemplary embodiment of the present invention. Morespecifically, these figures show the reduction in electromagneticcoupling between two antennas 110, 115 achieved by canceling theinterfering transmitting signal occurring on a dormant ornon-transmitting antenna 110 that is an interference recipient andcarrier of an interference signal.

The intensity of the white pattern on the black background shows thesimulated surface current distribution for a pair of compactfolded-dipole antennas 110, 115 spatially separated by λ/10 (0.1lambda). In one exemplary embodiment, the antennas 110, 115 illustratedin FIGS. 1 and 2 can be the compact folded-dipoles of FIGS. 3A and 3Band will be referred to as such with reference to FIGS. 3A, 3B, 4A, and4B.

FIG. 3A illustrates the surface current distribution with the system 300a operating in an uncompensated state. The unconfined surface currentshows crosstalk coupling between the antennas 110, 115 associated with alack of antenna isolation. The transmitting antenna 115 excites thedormant antenna 110 causing spreading or dispersion of surface currentbetween the two antennas 110, 115.

FIG. 3B illustrates the simulated result of applying crosstalkcancellation via the canceller 175 a as shown in FIGS. 1 and 2 anddiscussed above. That is, the canceller 175 a applies crosstalkcancellation to the dormant antenna 110 thereby improving performance ofthe transmitting antenna 115. As demonstrated by the minimal ornear-zero current distribution on the dormant antenna 110, the canceller175 a reduces the unintended coupling between the antennas 110, 115 to avalue that can approach zero. In other words, the confinement of thesurface current to the active antenna 115 correlates to improvedisolation of this antenna 115.

Turning now to FIGS. 4A, 4B, and 4C, these figures respectivelyillustrate simulated antenna field patterns 425, 450, 475 for a singleantenna 115 that is inherently isolated, a two-antenna system beforecrosstalk cancellation 300 a, and a two-antenna system after crosstalkcancellation 300 b in accordance with an exemplary embodiment of thepresent invention. Each of the figures presents its respective fieldpattern 425, 450, 475 as a three-dimensional plot. As will be understoodby those skilled in the art, the plots 425, 450, 475 graphicallyrepresent electromagnetic field patterns and convey information in anintuitive manner. Thus, these plots 425, 450, 475 complement the currentdensity illustrations 300 a, 300 b of FIGS. 3A and 3B discussed aboveand illustrate the beneficial results that the crosstalk canceller 175 acan provide.

The plot 425 of FIG. 4A presents simulated data from a singlefolded-dipole antenna 115 that is not subject to interference fromanother antenna 110. Specifically, the illustrated field pattern 425 isan output of a simulation of operating the transmitting antenna 115shown in FIGS. 3A and 3B without the presence of the adjacent dormantantenna 110. The field pattern 425 derived from operating this antenna115 in a fully isolated state provides a standard for evaluating theresults of applying a crosstalk canceller 175 a to an interfering pairof antennas 300 a. That is, the simulated single antenna 115 isinherently isolated from interference. The directivity of the antenna'sradiation pattern 425 is 4.9 dBi.

As will be appreciated by those skilled in the art, directivity is ameasure of the focus of an antenna coverage pattern in a givendirection. A theoretical loss-less antenna element, referred to as anisotropic element, has 0.0 dBi directive gain distributed in all threedimensions. That is, an isotropic antenna is a theoretical point sourcethat radiates power equally in all directions, resulting in a perfectspherical pattern.

In order to achieve higher directive gain in a direction of interest,most antennas focus or concentrate the antenna's field pattern in aspecific direction, such as towards a receiver, thereby maximizingenergy transfer. For example, most patch antennas have a beam patternthat is directed in a single direction to project a substantial portionof the energy perpendicular to the application plane.

The unit “dBi” refers to a decibel (“dB”) representation of the ratiobetween a given antenna's power and the corresponding power of anisotropic antenna's power, wherein “dB” denotes ten times the base-tenlogarithm of the ratio. Higher dBi values correspond to higher gain andthus more focus coverage. For example, an antenna that has 10 dB of gainin a specific direction provides ten-fold more gain in that specificdirection than would an isotropic antenna.

FIG. 4B shows the simulated pattern for a two antenna system 300 a wherethe second antenna 110 is dormant and placed λ/10 away from thetransmitting antenna 115 as illustrated in FIG. 3A and discussed above.The transmitting antenna 115 exhibits a radiation pattern with adirectivity of 3.9 dBi. Thus, the presence of the second interferingantenna 115 reduces the maximum gain of the pattern from 4.9 dBi to 3.9dBi.

FIG. 4C shows the simulated pattern for the two antenna system 300 b ofFIG. 3B resulting from applying crosstalk cancellation to the dormantantenna 110 via the crosstalk canceller 175 a as illustrated in FIG. 3Band discussed above. With the crosstalk canceller 175 a active, theantenna 115 outputs a radiation pattern with a directivity of 4.7 dBi.

Whereas the antenna pattern 450 of the active antenna 115 in thepresence of the uncorrected dormant antenna 110 exhibits reduced focusand distortion as compared to the single-antenna field pattern 425, thecorrected field pattern 475 resembles the single-antenna field pattern425. That is, the interference canceller 175 a redirects and reshapesthe transmitted beam of an active antenna 115 to achieve isolation andto meet a specified result, for example. The canceller 175 a furtherrestores the gain directivity to a value that is within 0.2 dBi of thedirectivity of a single antenna 115 that is inherently isolated. Thus,the simulated cancellation largely removes the interference that anactive antenna 115 imposes on an adjacent dormant antenna 110.

The beam restoration provided by the canceller 175 a can yield a gainimprovement of 3 to 4 dB for an antenna 115 in a design direction ofmaximum radiation. The systemic effect of these improvements can achievea four-fold to five-fold improvement in transmission distance, a 40%reduction in required antenna power, and a ten-fold improvement in biterror rate (“BER”), for example.

Turning now to FIG. 5A, this figure illustrates an exemplary system 500comprising two patch antennas 510, 515 in accordance with an exemplaryembodiment of the present invention. These antennas 510, 515 werefabricated on a substrate of FR4 material, which is a synthetic materialcommonly used for circuit boards. Versions of the antenna system 500were fabricated with spacing between the individual antennas 510, 515 ofλ/10, λ/8, λ/6, λ/4, and λ/2. That is, the physical distance between thepatch antennas 510, 515 for each of five fabricated systems 500 was,respectively, one tenth, one eighth, one sixth, and one half of thewavelength, lambda, of the transmitted communication signal. Whileeither of the antenna 510, 515 may be in a dormant or active state, theantenna 515 will be arbitrarily referred to as the transmitting antennawhile the antenna 510 will be arbitrarily referred to as the dormantantenna.

Turning now to FIG. 5B, this figure illustrates a graph ofrepresentative signal plots 565, 570, 575, 580, 585 for the patchantenna system 500 prior to interference cancellation in accordance withan exemplary embodiment of the present invention. In laboratory testingof each of the five antenna systems 500, one patch antenna 515transmitted excitation signals of varying frequency. At the same time,an instrument monitored the power coupled into the other patch antenna510 as a function of frequency. Thus, the plot 550 illustrates therelative coupling between the two antennas 510, 515 for frequenciesbetween 1 gigahertz (“GHz”) and 4 GHz (1×10⁹ Hz to 4×10⁹ Hz).

All of the signal plots 565, 570, 575, 580, 585 have a peak atapproximately 2.4 GHz, indicating that crosstalk coupling is strongestfor this frequency. The trend in the family of curves 565, 570, 575,580, 585 shows that the crosstalk interference effect increases withdecreasing spatial separation between the antennas 510, 515. Thecoupling for the different spaced antennas pairs 500 varies from −15 to−28 dB at 2.4 GHz. That is, the coupling plots 585, 580, 575, 570, 565for each of the antenna pairs 500 that have respectiveantenna-to-antenna separations of λ/2, λ/4, λ/6, λ/8, and λ/10,progressively intensifies as the separation between the antennas 510,515 lessens. The test data shows that the coupling is strongest for theλ/10-spaced patch antennas 510, 515.

In one exemplary embodiment of the present invention, the patch antennapair 500 operates in a WiFi application or complies with the standardsprovided by the Institute of Electronic and Electrical Engineers(“IEEE”) under the designation IEEE 802.11 or specifically the codingprotocols that paragraphs b or g of this specification provide. The IEEE802.11b standard describes enhancements to IEEE 802.11 to support datarates of 5.5 and 11 Megabits per second. The IEEE 802.11g standarddescribes protocols for wireless communication with 54 Megabits persecond of data at 2.4 GHz.

FIGS. 6A and 6B illustrate signal plots 600, 650 for a pair 500 of patchantennas 510, 515 before and after interference cancellation inaccordance with an exemplary embodiment of the present invention. Theplots 600, 650 present laboratory test data for the patch antenna pair500 illustrated in FIG. 5A and discussed above.

The plot 600 of FIG. 6A shows two transmit power spectra 610, 620 forthe λ/10-spaced patch antenna pair 500. The trace 620 presents test dataacquired prior to applying interference cancellation. In contrast, thetrace 610 presents test data acquired while applying interferencecancellation according to an exemplary embodiment of the presentinvention. Specifically, the test conditions included an application ofinterference cancellation that was in keeping with the cancellationprovided by the exemplary canceller 175 a discussed above with referenceto FIGS. 1-4.

A fixed level of input power fed the transmit patch antenna 515. Thepatch antenna 510 was dormant during the tests and interfered with thefunction of the active antenna 515. Trace 620 presents the antenna'stransmitted power without interference cancellation. In contrast, trace610 presents the antenna's transmitted power during interferencecancellation. The difference 625 between the two test traces 610, 620 isapproximately 1.08 dB. That is, under laboratory test conditions, theinterference canceller 175 a provided an improvement in antenna gain ofapproximately 1.08 dB. Thus, crosstalk cancellation provides the antennasystem 500 with a measured improvement in transmitted power.

The plot 650 of FIG. 6B shows measured data of the electromagneticsignal on the dormant antenna 510 before and after crosstalkcancellation. The trace 660 was generated by measuring the signal on thedormant antenna 510 without interference cancellation while the activeantenna 515 transmitted RF communication signals by radiating anelectromagnetic field. Conversely, the trace 670 shows the signalcaptured from the dormant antenna 510 while the active antenna 515output a signal and the canceller 175 a suppressed interference. Thedifference 680 between these two traces 660, 670 shows that thecanceller 175 a provided a 32 dB improvement in antenna isolation. Thatis, the application of crosstalk cancellation significantly reducedundesirable power transfer from the transmitting antenna 515 to thedormant antenna 510.

Turning now to FIG. 7, this figure illustrates an exemplaryimplementation of a system 700 comprising two crosstalk cancellers 750a, 750 b coupled in a parallel arrangement between two antennas 110, 115in accordance with an embodiment of the present invention. The system700 of FIG. 7 and the system 100 illustrated in FIG. 1 and discussedabove can comprise the same antennas 110, 115 and antenna feed lines160, 165 and can receive communication impairment from the same forms ofcrosstalk interference 180, 185, 190. However, the operational modes andcancellers 175, 750 of these systems 100, 700 can be distinct.

Referring to FIG. 7, the cancellers 750 a, 750 b can addressinterference in diversity antenna systems as well as interference onsystems having antennas that transmit at different frequencies. That is,the antennas 110, 115 of the system 700 can each transmit signals at adistinct frequency. Further, the system 700 can simultaneously sendsignals from both antennas 110, 115 or can simultaneously receivesignals from the antennas 110, 115 during crosstalk cancellation. Thecrosstalk cancellers 750 a, 750 b can provide in-band and/or out-of-bandinterference cancellation. The resulting crosstalk cancellation canimprove receiver sensitivity and radiation pattern.

The cancellers 750 a, 750 b connect between the antennas 110, 115 in aparallel arrangement. Canceller 750 a applies crosstalk cancellation tothe antenna 115 via the feed line 165, while canceller 750 b providescancellation to the antenna 110 via the feed line 160. The resultingcanceller arrangement provides bi-directionality for each of theantennas 110, 115. In this arrangement, both cancellers 750 a, 750 b canconcurrently cancel interference at the same time that both antennas110, 115 are actively transmitting signals. Thus, each of the antennas110, 115 can be a recipient antenna and a transmitting antenna at thesame time.

Canceller 750 a taps a reference signal off the feed line 160 of theantenna 110 and processes this reference signal to generate acancellation signal that it applies to the feed line 165 of the antenna115. The application of the cancellation signal to the recipient antenna115 cancels or suppresses interference imposed on the recipient antenna115 by the transmitting antenna 110.

Canceller 750 b functions in a corresponding manner but in the oppositedirection, tapping a reference signal from the antenna 115 and applyinga generated cancellation signal to the antenna 110. In this operationaldirection, the antenna 115 functions as the transmitting antenna 115 andthe antenna 110 functions as the recipient antenna 110.

Turning now to FIG. 8, this figure illustrates an exemplary functionalblock diagram of a system 700 having crosstalk cancellers 750 a, 750 bcoupled between two antennas 110, 115 in accordance with an embodimentof the present invention. The system 700 of FIG. 8 can be the samesystem 700 illustrated in FIG. 7 and discussed above.

The components and layout of the crosstalk canceller 750 b aretransposed with respect to the crosstalk canceller 750 a to support theunidirectional crosstalk cancellation of each canceller 750 a, 750 b. Inone exemplary embodiment of the present invention, a single integratedunit comprises both cancellers 750 a, 750 b.

In one exemplary embodiment, both cancellers 750 a, 750 b have the samelayout and are essentially identically. Thus, each of the cancellers 750a, 750 b can be a copy of a canceller module that has pin outs for thesplitters 840, 850 and the summation nodes 860, 870. In this scenario,which applies to both antennas 110, 115 operating at the same frequency,the pin outs of each canceller module can be connected to theappropriate antenna feed lines 160, 165 to provide the systemarchitecture shown in FIG. 8. However, if each antenna 110, 115 operatesat a distinct frequency, each canceller 750 a, 750 b has a uniqueemulation filter 810 corresponding to the frequency of operation of therespective antenna 110, 115.

In one exemplary embodiment of the present invention, the system 700comprises transmitter and receiver electronics (not shown) coupled toeach of the antenna feed lines 160, 165. Each antenna 110, 115 can be atransceiver antenna that both sends and receives wireless signals. Aduplexer (not shown) can separate ingoing and outgoing signals fordirection to the appropriate circuit paths. The duplexer can directincoming signals from antenna 110 to the receiver and can directoutgoing signals from the transmitter to the antenna 110, for example.PAs (not shown) can amplify outgoing signals that radiate from eachantenna 110, 115. A PA is not disposed between the duplexer and itsassociated antenna 110, 115, as the signal path spanning between theduplexer and the antenna 110, 115 is bidirectional, whereas the PAhandles signals in a single direction. Rather, the PA is on thetransmitter side of the duplexer, opposite the antenna. In other words,components that are not bidirectional, such as PAs, typically are notdisposed between a duplexer and its respective antenna 110, 115.

The functional blocks and operation of the canceller 750 a will now bedescribed in overview fashion. The splitter 840 samples the transmittedsignal on the feed line 160 of the transmitting antenna 110. The model825 processes the sample to generate an estimate of the interferencesignal imposed on the recipient antenna 115 by the transmitted signal onthe antenna 110. The phase adjuster 220, the delay adjuster 225, and theVGA 260 of the model 825 respectively adjust the phase, timing, andamplitude of the sampled signal to match the interference on the antenna115 for application at the summation node 870. The emulation filter 810models channel coupling and is tunable in order to compensate for driftsin the channel's center frequency.

The controller 820 adjusts the phase adjuster 220, the channel emulationfilter 810, the delay adjuster 225, and the VGA 260 based on a feedbackprovided by the power detector 240. The controller 820 further controlsthe voltage controlled oscillator (“VCO”) 830. Upon the controller'scommand, the VCO 830 generates pilot signals that the coupler 860injects into feed line 160 of the antenna 110. Via the splitter 850 andpower detector 240, the controller monitors the antenna-to-antennacrosstalk response to the pilot signal stimuli. The controller 820minimizes the received pilot signal which couples via air or otherinterference mechanism and also undergoes processing by the signalprocessing circuit 825. The model 825 is adapted to cancel the pilotsignals, which are out-of-band in comparison to the recipient antenna'soperating frequency 115. Pilot signals may not be necessary fordiversity antenna applications.

Based on the monitored response, the controller 820 dynamically refinesthe model 825 by adjusting the phase adjuster 220, the emulation filter810, the delay adjuster 225, and the VGA 260. The controller 820comprises logical elements, such as hardwired, fixed, or programmablelogic. The controller 820 usually comprises a microcontroller,microprocessor, microcomputer, or other computing processor, such as anASIC. In addition to such logical elements, the controller can comprisesupporting circuitry, interface electronics, power supplies, and memory,for example.

The functional blocks of the canceller 750 a will now be discussedindividually. The splitter 840 obtains a sample of the transmittedsignal on feed line 160 that conveys the communication signal, in theform of RF energy, to the antenna 110. The sample signal can comprise acommunication signal intended to radiate from the antenna 110. Thesplitter 840 can be a passive directional coupler or an active circuit,as discussed above with reference to the splitter 210 of the system 100illustrated in FIG. 2. Further, the splitter 840 can be essentially thesame component as the splitter 210. The splitter 840, the splitter 850,the summation node 860, and the summation node 870 can each comprise acoupler and can also comprise three signal ports.

As discussed above with reference to the splitter 210 of FIG. 2, thesplitter 840 should have impedance characteristics that match theimpedance characteristics of the other components coupled to feed line160 and should be not exhibit excessive loss characteristics. Further,the splitter 840 should have high impedance at the tap off point toavoid drawing excessive power from the feed line 160.

If loss compensation in the form of an amplifier stage or other devicethat is not bidirectional is introduced into the signal path, suchdevice should be disposed on a section of the signal path that has aunidirectional signal flow corresponding to the device's directionality.Thus, loss compensation, if needed, should be applied on thetransmitter/receiver side of any duplexers that the system 700 maycomprise, rather than between a duplexer and its associated antenna.

In one exemplary embodiment of the present invention, the splitter 840is disposed between the duplexer and the antenna 110. In thisconfiguration, the canceller 750 a can model any coupled interferencenon-linearity introduced to the system 700 by the duplexer and/or anassociated PA.

Alternatively, the splitter 840 may be disposed between the duplexer andthe PA, which as discussed above is on the opposite side of the duplexerwith respect to the antenna 110. The splitter 840 could also be disposedbefore the PA. However, this configuration is not desirable for mostapplications as the non-linearity introduced by the PA to the systemwill not be modeled by the canceller 750 a.

The preferred position of the summation node 870 is between the antenna115 and the duplexer. If the summation node 870 is placed after theduplexer, i.e. between the duplexer and the LNA, then the canceller 750a will improve the receiver sensitivity but may not add sufficientcontribution in improvement to the aggressing antenna signal integrity(i.e. beam shape, gain, directivity) as the other configuration. Placingthe summation node 870 after the LNA typically will not yieldimprovement of the aggressing antenna signal integrity as the LNA isunidirectional. The improvements are on receiver sensitivity of therecipient antenna 115.

The splitter 840 provides the signal sample to the phase adjuster 220.As discussed above with reference to FIG. 2, the phase adjuster 220adjusts the phase of the cancellation signal to match the phase of theinterfering signal on the feed line 165 at point of applying thecancellation signal thereto. Also as discussed above, the phase shifter220 can provide phase coherency if the summation node 870 issubtractive. And, the phase shifter 220 can provide a 180° phase shiftif the summation node is additive.

The phase adjuster 220 outputs a signal to the emulation filter 810,which may be referred to as a band-pass (“BP”) channel emulation filter.The emulation filter 810 models the channel coupling and is also tunablein order to compensate for any drifts in channel center frequency.

As shown by the shape of the plot 550 of FIG. 5B, which is discussedabove, the coupling effect between two antennas 110, 115 can exhibit adefined frequency response. Aging, associated with antenna oxidation forexample, may vary the center frequency and coupling of the closelyspaced antennas. The rapid changes in the frequencies above and below2.4 GHz is attributable to the noise floor or dynamic range of themeasurement system. A frequency deviation, due to an environmental oraging related change can cause a variation in intensity and frequencycontent of the interference signal. By modeling the frequency responseof the coupling effect or channel, the emulation filter 810 provides anemulated signal that is similar to the interference on the feed line 165despite changes in the excitation signal on the source antenna 110. Thatis, the emulation filter 810 models the transfer function of thecoupling channel in the frequency domain to provide cancellation signalshaving frequency dependent characteristics that match the actualinterference on the antenna 115.

In one embodiment of the proposed invention, the emulation filter 810comprises lumped elements and varactor diodes. The varactor diodesfacilitate changing the center frequency of the emulation channel. In analternative embodiment of the invention, the emulation band pass filter810 is a Finite Impulse Filter (“FIR”), such as a tapped delay linefilter. The taps and the taps spacing of such an FIR are extracted fromthe closely spaced antenna coupling channel characteristics. In order toachieve a high level of antenna coupling cancellation for improvedsignal integrity of the system 700, the emulation filter 810 shouldmatch, in trend, the coupling channel characteristics within the band ofinterest.

Commonly owned U.S. Nonprovisional patent application Ser. No.10/911,915, entitled “Method and System for Crosstalk Cancellation” andfiled on Aug. 5, 2004, discloses a viable exemplary tapped delay linefilter system for modeling a crosstalk transfer function. In oneembodiment, the tapped delay line filter comprises a plurality of delayelement coupled to a plurality of variable gain amplifiers. That patentapplication further discloses a viable exemplary system and method foradapting a crosstalk model using a controller that monitors channelsignals. The disclosure of U.S. patent application Ser. No. 10/911,915is hereby fully incorporated by reference.

One or more of the phase adjuster 220, the VGA 260, the delay adjuster225, and the emulation filter 810 can each be controlled and/or adjustedusing a method and/or system disclosed in U.S. patent application Ser.No. 10/108,598 or U.S. patent application Ser. No. 10/620,477, discussedabove with respect to FIG. 2. The parameters of these devices 220, 260,225, 810 can be determined by treating each parameter as a variable thatis swept through its range of potential values following the disclosuresof these patent applications, for example.

The output of the emulation filter 810 feeds into the input of the delayadjuster 225. The delay adjuster 225 matches the group delay of theinterference on the antenna 115 with the group delay of the emulatedcancellation signal that is applied at summation node 870 to the feedline 165.

The VGA 260 receives the output of the delay adjuster 225 and adjuststhe emulated signal's amplitude to match the amplitude of theinterference signal at summation node 870. In contrast to the emulationfilter's modeling of the frequency response of the crosstalk orinterference channel, the VGA 260 shifts the level of the emulatedsignal to provide an amplitude match with the interference signal on thefeed line 165. By modeling the frequency response of the crosstalkeffect, the emulation filter 810 produces an emulated signal having awaveform shape that is similar to the waveform shape of the interferencesignal on the feed line 165. On the other hand, the VGA 260 applies gainto the emulated signal to impart it with amplitude or intensity that issubstantially similar to the crosstalk interference.

The summation node 870, which can be a directional coupler or an activecircuit, applies the emulated signal to the feed line 165 to cancel ornegate the interference. As discussed above regarding the summation node290 illustrated in FIG. 2, the summation node 870 should have impedancecharacteristics that match the impedance characteristics of the othersystem components and should not introduce excessive loss onto the feedline 165. The summation node 870 can be essentially the same summationnode 290 of the system 100 illustrated in FIG. 2 and discussed above.

The splitter 850, which is coupled to the feed line 165 of the antenna115, samples the cancelled signal and feeds it to the power detector240, which monitors the power or energy of the cancelled signalassociated with the cancelled pilot signals. That is, the splitter 850and the power detector 240 gauge the level of any residual orpost-cancellation interference that remains on the antenna 115. Thecontroller 820 uses this monitored signal as feedback for adjusting thephase adjuster 220, the emulation filter 810, the delay adjuster 225,and the VGA 260.

Under control of the controller, the VCO 830 generates test signals orpilot signals that the summation node 860 injects into the signal pathof the feed line 160 of the antenna 110. The canceller 750 a monitorsthe response of the system 700 to these pilot signals to adapt thecancellation signal to effectively cancel the interference. Morespecifically, the canceller 750 a monitors residual interferenceassociated with the pilot signals.

The controller 820 controls, refines, or optimizes the operation of theinterference canceller 750 a using an adaptive approach that learns thevalue of the magnitude, phase, and delay of the interfering signal byminimizing the energy of the coupled interference. In other words, thecontroller 820 dynamically adjusts the phase adjuster 220, the channelemulation filter 810, the delay adjuster 225, and the VGA 260 in anadaptive manner that reduces or minimizes the energy of the interferenceon the antenna 115. As discussed above, the splitter 850 and the powerdetector 240 monitor the level of interference energy.

Exemplary embodiments of the system 700 can provide interferencecancellation in three operational states. In one embodiment, the system700 operates in a diversity antenna application, whereby the antenna 115is dormant and the antenna 110 is actively transmitting. In such adiversity application, the canceller 750 a can cancel crosstalk imposedon recipient antenna 115 without using pilot signals to characterize thecoupling channel. Thus, this first embodiment can correspond to themodes of operation of the system 100 illustrated in FIGS. 1 and 2 anddiscussed above.

In a second embodiment, the system 700 operates with the antenna 115 andthe antenna 110 operating at distinct frequencies. In this scenario, thecommunication signals transmitting on the antenna 110 couple onto theantenna 115 via a coupling channel. The canceller 750 a injects twopilot signals onto the antenna 110, which couple onto the antenna 115.One of these pilot signals has a frequency above the operating frequencyof antenna 115, while the other pilot signal has a frequency below theoperating frequency of the antenna 115. The canceller uses these pilotsignals to address the interference.

In the third embodiment, the canceller 750 cancels crosstalk occurringwith the antenna 110 and the antenna 115 operating at essentially thesame frequency. The third exemplary embodiment will be discussed indetail. Those skilled in the art will appreciate the applicability ofthe discussion to the second embodiment described in the immediatelypreceding paragraph.

With the antenna 110 and the antenna 115 operating at essentially thesame frequency, two test or pilot signals inserted onto the antenna 110can characterize the coupling channel. The cancellation signal providedby the canceller 750 a is continuously updated via two the pilotsignals, one having a frequency higher than the communication band ofthe system 700 and one having a frequency lower that the band. For asystem that communicates at 2.4 GHz, one pilot signal can have afrequency of 2.45 GHz while the other pilot signal has a frequency of2.35 GHz, for example. Spectrally positioning the pilot signals outsidethe communication band avoids interference between the pilot signals andthe communication signals. The VCO 830 alternately outputs thehigh-frequency pilot signal and then the low-frequency pilot signal.Thus, at any particular time during the canceller's operation, thecoupler 860 can be injecting one of the pilot signals and the controller820 can be refining the canceller's operation based on the resultingpower measurements from the power detector 240. In one embodiment, thecanceller 750 a intermittently outputs the pilot signals.

Turning now to FIG. 9, this figure illustrates a graph of an exemplaryfamily of curves 905, 910, 915, 920, 925, 930 of interference couplingbetween two antennas 110, 115 as a function of frequency for variousphase alignment values in accordance with an embodiment of the presentinvention.

The frequency range of the plot 900, which extends from 2.4 to 2.5 GHz,can be an exemplary frequency band over which the canceller 750 aminimizes interference. That is, the canceller 750 a may cancelcrosstalk interference across a frequency band that spans from 2.4 to2.5 GHz.

The curve 970 shows the overall frequency response of the couplingchannel. Thus, the antenna 110 couples to antenna 115 a ratio of itsenergy that ranges between approximately −18.5 dB and approximately−13.5 dB for the frequency band.

The curves 905, 910, 915, 920, 925, 930 each shows the coupling ratio,in dB, for respective phase alignments of 110°, 90°, 70°, 10°, 50°, and30° following cancellation. Thus, each of these curves 905, 910, 915,920, 925, 930 illustrates the resulting level of crosstalk that thecanceller 175 a can achieve by adjusting the phase of the cancellationsignal as indicated. For example, if the phase adjuster 220 adjusts thephase of the cancellation signal to 110°, the crosstalk coupling will beapproximately −26.3 dB at 2.4 GHz, less than −40 dB at 2.44 GHz, and −17dB at 2.5 GHz.

The graph 900 further illustrates spectral representations of twooverlaid pilot signals 970, 950, one having a frequency near 2.4 GHz andone having a frequency near 2.5 GHz. As discussed above, the canceller750 a can adjust the phase of the cancellation signal based on therelative coupling of these pilot signals 940, 950 between the antennas110, 115.

Adapting the canceller system using the pilot one signal 940 results ina 90° phase adjustment for optimal cancellation. That is, if thecontroller 820 manipulates the phase adjuster 220 to minimize thecrosstalk coupling of the pilot one signal 940, the controller 820 willselect 90° as the optimal phase. The 90° degree phase setting is optimalfor the pilot one signal 940 because the 90° curve 910 has the lowestcoupling at the frequency of the pilot signal 940.

However, for the pilot two signal 950 a 90° adjustment in phase is notan optimal solution. At the frequency of the pilot two signal 950, a 90°phase adjustment in the cancellation signal provides an interferencecoupling of approximately −19 dB. That is, the 90° phase adjustmentcurve 910 has a value of approximately −19 dB at the frequency of thepilot two signal 950. At the frequency of the pilot signal two 950, aphase adjustment of 30° provides an improved level of interferencesuppression according to the curve 930.

By adapting the cancellation signal based on the two pilot signals 940,950, rather only one, the controller can provide effective cancellationacross a band of frequencies, such as for the range between 2.4 GHz and2.5 GHz. In one exemplary embodiment of the present invention, thecontroller 820 averages the phase selection for the pilot one signal 940with the phase selection for the pilot two signal 950. For example, thecontroller 820 can average the 90° phase adjustment with the 30°adjustment to compute a 60° phase adjustment.

Rather than a simple average, the controller 820 can also implement aniterative error minimization process to select a phase that provideseffective cancellation across a frequency band of interest. According tothe plot 900, a phase adjustment of approximately 70° provides optimalminimization of the coupling signal. To identify this 70° operatingpoint, the controller 820 can use the 60° phase adjustment as a startingpoint and make incremental phase adjustments thereafter. If the feedbacksignal from the power detector 240 increases as a result of theincremental adjustment, the controller 820 implements a differentincremental phase adjustment. In this manner, the controller 820 canstart at 60° and adapt via iteration until it finds the optimal 70°degree phase adjustment. The controller 820 can continually refine thecancellation signal during normal operations, to respond to changingconditions such as environment effects and frequency drift.

The controller 820 can also use other empirical search or optimizationmethodologies known to those skilled in the art. In one exemplaryembodiment of the present invention, a coordinate-descent approach, asdescribed in U.S. patent application Ser. No. 10/620,477, discussedabove, provides search and optimization to identify acceptable modelparameters based measuring the system's response to test signal stimuli.

Turning now to FIG. 10, this figure illustrates a flowchart of anexemplary process 1000, entitled Cancel Crosstalk, for cancelingcrosstalk or interference on an antenna 115 according to an embodimentof the present invention. The steps of Process 1000 will be discussedwith exemplary reference to the system 700 of FIGS. 7 and 8, which arediscussed above.

Certain steps in this process or the other exemplary processes describedherein must naturally precede others for the present invention tofunction as described. However, the present invention is not limited tothe order of the steps described if such order or sequence does notalter the functionality of the present invention. That is, it isrecognized that some steps may be performed before or after other stepsor in parallel with other steps without departing from the scope andspirit of the present invention.

At Step 1010, the first step in Process 1000, the transmitting antenna110 transmits a communication signal. A transmitter (not illustrated)can supply the transmitting signal to the feed line 160. Thecommunication signal can be encoded with voice information or data, forexample. The transmitting antenna 110 outputs a radiation pattern that aremote communication device (not illustrated) may receive.

At Step 1015, a crosstalk effect 180, 185, 190 couples energy of thetransmitted communication signal from the transmitting antenna 110 ontothe recipient antenna 115. An interference signal, carried on therecipient antenna 115, comprises the interference. As discussed above,the recipient antenna 115 may also be transmitting communication signalscontemporaneous with carrying the imposed interference.

At Step 1020, the interference signal on the recipient antenna 115interferes with the operation or function of the transmitting antenna110. The interference can distort the field pattern of the transmittingantenna 115 or compromise the integrity of the communication signaland/or receiver sensitivity.

At Step 1025, the canceller 175 a samples the communication signal onthe transmitting antenna 110. Specifically, the splitter 840 taps off aportion of the signals on the feed line 160 of the transmitting antenna110.

At Step 1030, the model 825 of the canceller 750 a processes the sampleof the communication signal. Based on this processing, the model 825outputs an estimate of the interference signal that the recipientantenna 115 carries. A cancellation signal can comprise the estimate.The model 875 processes the sample signal with the phase adjuster 220,the emulation filter 810, the delay adjuster 225, and the VGA 260. Thephase adjuster 220 applies a phase delay to the sample signal. Theemulation filter 810 filters the sample signal according to a filterparameter. The delay adjuster 225 delays the sample signal by a time.The VGA 260 applies a gain to the sample signal to provideamplification.

At Step 1035, summation node 870 applies the estimate or cancellationsignal to the recipient antenna 115. At Step 1040, the cancellationsignal mixes with and cancels the interference signal on the recipientantenna 115. The cancellation signal typically cancels a substantialportion of the interference signal, but not necessarily all of it. Thatis, a residual level of interference may remain un-canceled.

At Step 1045, the controller 820 outputs a signal to the VCO 830. Inresponse, the VCO 830 generates a test or pilot signal 940, 950 of knownfrequency, typically distinct from the frequency of the communicationsignal. The node 860 places the test signal 940, 950 on the feed line160 of the transmitting antenna 110.

At Step 1050, the test signal 940, 950 couples onto the recipientantenna 115 via one or more crosstalk effects 180, 185, 190. Forexample, a portion of the energy in the test signal 940, 950 maytransfer to the recipient antenna 115 via free space coupling.

At Step 1055, the splitter 850 taps a portion of the interference due tothe test signal 940, 950 from the feed line 165 of the recipient antenna115. The power monitor 240 measures the power level of the extractedsignal. The controller 820 analyzes the extracted signal. Specifically,the controller 820 determines the level of power in the extracted signalat the frequency of the test signal 940, 950. A more detailed discussionof the controller's processing or analysis of the extracted signal ortest signal 940, 950 is provided above with reference to FIGS. 7, 8, and9.

At Step 1060, the controller 820 adjusts the modeling, the phase shift,the delay, and the gain in a dynamic manner in response to Step 1055.That is, the controller 820 adjusts the respective parameters oroperating points of the phase adjuster 220, the emulation filter 810,the delay adjuster 225, and the VGA 260. These adjustments improve themodel's function and yield iterative improvements or refinements in thecancellation signal's effectiveness. The more detailed discussion of theadaptation is provided above with reference to FIGS. 7, 8, and 9.Following Step 1060, Process 1000 iterates Steps 1010-1060.

Although a system in accordance with the present invention can comprisea circuit that cancels, corrects, or compensates for crosstalk imposedon one communication signal by another signal, those skilled in the artwill appreciate that the present invention is not limited to thisapplication and that the embodiments described herein are illustrativeand not restrictive. Furthermore, it should be understood that variousother alternatives to the embodiments of the invention described heremay be employed in practicing the invention. The scope of the inventionis intended to be limited only by the claims below.

1. A method for suppressing an interference signal imposed by a first antenna on a second antenna, comprising: sampling a transmitted signal on the first antenna; processing the sampled signal according to a parameter to generate an estimate of the interference signal; applying the estimate of the interference signal to the second antenna to suppress the interference signal; and varying the parameter in response to monitoring the suppressed interference signal.
 2. The method of claim 1, wherein: the interference signal has a first phase; the estimate of the interference signal has a second phase; the parameter comprises a phase shift; processing the sampled signal comprises applying the phase shift to the sampled signal; and the varying step comprises adjusting the phase shift to match the second phase to the first phase.
 3. The method of claim 1, wherein processing the sampled signal comprises filtering the sampled signal with a filter having a frequency response, and wherein varying the parameter comprises adjusting the frequency response.
 4. The method of claim 1, wherein the estimate of the interference signal comprises a cancellation signal.
 5. The method of claim 1, wherein: the processing step comprises: applying a phase shift to the sampled signal; filtering the sampled signal according to a filter parameter; delaying the sampled signal by a time; and amplifying the sampled signal according to a gain; and varying the parameter comprises adjusting the phase shift, the filter parameter, the time, and the gain.
 6. The method of claim 1, wherein the transmitted signal comprises a test signal and a communication signal.
 7. The method of claim 1, further comprising the step of transmitting, on the first antenna a first test signal having a first frequency, a second test signal having a second frequency, and a communication signal having a third frequency, wherein the third frequency is between the first frequency and the second frequency, and wherein the sampling step comprises sampling the first transmitted test signal and sampling the second transmitted test signal.
 8. The method of claim 1, wherein the interference signal is imposed by the first antenna on the second antenna via an interference effect and wherein the method further comprises the steps of: generating a pilot signal; applying the pilot signal to the first antenna; transferring at least a portion of the pilot signal from the first antenna to the second antenna via the interference effect; and specifying a model of the interference effect based on monitoring the transferred portion of the pilot signal, wherein the transmitted signal comprises a communication signal, and processing the sampled signal comprises applying the specified model to the communication signal.
 9. The method of claim 1, wherein monitoring the suppressed interference signal comprises tapping power from a feed line of the second antenna and measuring the tapped power.
 10. A method for reducing interference on an antenna system, comprising: transmitting a test signal on a first antenna; coupling a portion of the test signal from the first antenna to a second antenna via an interference effect; defining a model of the interference effect based on processing the test signal; responsive to transmitting a communication signal on the first antenna, coupling the interference onto the second antenna via the interference effect; outputting an estimate of the interference in response to processing the communication signal with the model; and applying the estimate to the second antenna to reduce the interference.
 11. The method of claim 10, wherein processing the test signal comprises monitoring the portion of the test signal coupled to the second antenna.
 12. The method of claim 10, wherein the interference effect comprises free space coupling.
 13. The method of claim 10, wherein the interference effect comprises dielectric leakage.
 14. The method of claim 10, wherein the interference effect comprises surface wave coupling.
 15. The method of claim 10, wherein transmitting the test signal on the first antenna comprises feeding the test signal onto a feed line of the first antenna via a first coupler and wherein applying the estimate to the second antenna comprises feeding the test signal onto a feed line of the second antenna via a second coupler.
 16. The method of claim 10, wherein applying the estimate to the second antenna comprises subtracting the estimate from the interference and the portion of the test signal coupled to the second antenna via the crosstalk effect.
 17. The method of claim 10, wherein the model comprises a filter and wherein defining the model comprises adjusting the filter.
 18. A system, for canceling a signal coupled onto a dormant antenna by an active antenna, comprising: a first coupler, comprising a port that connects to a feed line of the dormant antenna, for feeding a sample of the signal to a signal processing circuit; and a second coupler comprising a port for feeding a cancellation signal to the feed line, wherein the signal processing circuit generates the sampled signal based on amplifying and shifting the sampled signal.
 19. The system of claim 18, wherein: amplifying the sampled signal comprises applying a gain to the sampled signal; shifting the sampled signal comprises applying a phase shift to the sampled signal; and the system further comprises: a third coupler for obtaining a feedback signal from the feed line; and a controller for adjusting the gain and the phase shift based on the feedback signal.
 20. The system of claim 18, wherein the first coupler comprises a splitter and the second coupler comprises a summation node. 